The broad, long-term objective of this Phase II grant proposal is to improve accuracy of breast cancer diagnosis. Specifically, this Phase II grant proposal is for clinical testing of a new technology that will promote national standardization of Her2 quantification. This is of importance for proper patient management. Numerous studies have shown that clinical laboratory measurement of Her2 by immunohistochemistry is fraught with errors. Our technology for the development of Analyte Controls will be the first nationally standardized and reproducible test material for cellular analytes, such as Her2, measured in tissue biopsies. In this Phase II proposal, we will bring Her2 Analyte Controls to the clinic, through five Specific Aims. In Specific Aim 1, we build on the Phase I feasibility work by finishing the Her2 Analyte Controls so that they will be applicable for all FDA-approved Her2 tests. In Aim 2, we finish a simple, low-cost microscope slide scanner that laboratories will use to quantify the controls. We then will calibrate our Analyte Controls to specific molar concentrations of cellular Her2 (Specific Aim 3). In this way, the Analyte Controls technology can foster inter-laboratory standardization by serving as a tool for expressing patient results in tems of molar concentration, something that is not presently possible. Specific Aims 4 and 5 involve clinical testing. First, we will survey a national sample of clinical histopathology laboratories (Specific Aim 4), to identify the mean and standard deviation of Her2 immunostaining sensitivity. To do this, we have recruited the involvement of a national proficiency testing agency, which will send out our Analyte Controls to all of their participants. Lastly, we will test the Analyte Controls in five New England hospital clinical histopathology laboratories, for a period of six months. We expect that this data will ultimately be used for FDA submission by our commercial partner and the development of new national standards for tissue quantification of cancer analytes.